Fill-resistant flexible abrasive sheet



"ited brats The present invention relates to flexible coated abrasive sheets. More particularly, this invention relates to abrasive sheet structures such as coated abrasive belts and similar articles which are especially suitable for use in leather sanding operations.

In leather sanding operations, flexible abrasive sheet structures are employed mainly to even off the surface of the leather and to prepare a uniform surface for the subsequent absorption of colors in the preparation of leather articles. Such structures are also widely used to provide a suede surface on leather. However, difficulty often is encountered in these and other leather sanding operations in that abrasive sheet structures ordinarily are readily filled or clogged by leather particles abraded and removed from the leather surface. This is true even though the active abrading surface of the abrasive sheet or belt is continuously brushed or otherwise mechanically scrubbed, as an integral part of the operation, in an effort to keep the sheet as unfilled and unclogged as possible. Of course, by becoming so filled or clogged the abrasive structures are rendered prematurely useless because of loss of aggressiveness, even though the abrasive grains themselves are essentially undulled. This problem of the premature filling and consequent necessary disposal of abrasive sheets and belts in leather sanding operations has long beset that industry.

The provision of novel effective coated abrasive sheet structures which are highly fill-resistant to leather particles and which are capable of being readily brushed clean by conventional mechanical action, if they do become filled, is thus an important objective of the present invention.

Various means have been suggested for rendering abrasive sheets fill-resistant. Abrasive sheets have been sparsely coated with mineral to provide a so-called opencoat structure, but these abrasive articles have been found to be generally unsuitable in grain leather sanding operations. Even though they have an open structure, they are not particularly fill-resistant to abraded away leather particles (as opposed to other types of abrasive detritus). Moreover, open-coat structures tend to leave a coarse non-uniform finish unsuitable to subsequent coloring and finishing operations.

It has also been suggested that an abrasive sheet of improved fill-resistance might be obtained by applying increased amounts of abrasive binder, thereby raising the total binder to abrasive mineral ratio Well over that normally employed for an abrasive structure of the type, grit size, etc. to be used. The basis of this approach lies in filling to a high degree the spaces or valleys between the abrasive grains, so the latter would not protrude, relatively, as far from the sheet. This approach of raising the binder:mineral ratio has fallen far short of a practical and successful solution. Ordinarily if the adhesive binderzmineral ratio is raised to the point where the sheet becomes very fill-resistant, the abrasive particles are so buried that the sheet loses the aggressiveness necessary to produce an even surface condition in the leather. This is true even though a highly aggressive abrasive surface is not required in leather sanding.

By the term binder herein, we are referring to part or all the glue, adhesive, and/r resin materials which serve to bond the abrasive mineral to the sheet, including the so-called make-coat, sand-size coats, etc.

3,il43,73 Patented July 10,v 1962 In accordance with the present invention, a novel flexible coated abrasive sheet which is highly fill-resistant to leather is produced by employing a special binder composition at the abrading surface of the sheet. The special binder composition, however, is not singly what produces the desired feature in our structures. As a further, and conjunctive structural feature, the special binder composition is utilized in a particular physical relationship to the abrasive mineral grains of the sheet, all as more particular- 1y described hereinafter. Indeed, We have found it is not sufficient to employ the special binder composition in the manner in which abrasive binders generally are utilized in abrasive sheets of conventional type.

In the special binder composition of our structures, we employ or incorporate an oxy-containing compound within an otherwise conventional abrasive binder, the well-known phenol-aldehyde resin binders being preferred. Such oxy-compounds are exemplified in the form of aliphatic polyhydric alcohols and aliphatic polyethers. Among the many operable compounds are glycols, such as ethylene glycol, propylene glycol, trimethylene glycol, hexylene glycol, and octylene glycol; ether alcohols, such as polyethylene glycol, .diethylene glycol, polypropylene gloycol, and butylcarbitol; other polyhydric alcohols, such as sorbitol, pentaerythritol, triethanolamine, polyvinyl alcohol, and glycerol; cyclohexanepolyols, such as 1,3,5- cyclohexanetriol, and inositol; various ether and ester derivatives of polyethers, such as alkylphenyl-ethers of polyethylene glycol and .dilaurate esters of polyethylene glycols.

As previously mentioned, it has been found that the desirable fill-resistance and allied characteristics in the abrasive sheet structures hereof do not inevitably (or even usually) result from use only of the oxy-containing binder composition. In conjunction therewith an unusually high ratio of total abrasive binder composition to abrasive mineral is utilized which substantially exceeds the maximum vbinderzrnineral ratio over that normally employed heretofore for the abrasive structure of the type, grit size, etc. desired. However, it is unnecessary to employ such a high ratio that the abrading aggressiveness of the sheet structures, in leather sanding operations, is impaired.

The oxy-cornpounds in the abrasive binder of our structures are present at the surface of the sheet structure. They may be presentat the surface only, such as where the oxy-containing binder composition is applied as the sandsize over some standard make-coat, or even as a super-size applied over a conventional sandsize. If desired, theentire abrasive binder may contain the oxycompound. In the interest of economy, however, we ordinarily prefer to employ the oxy-compound' only in the surface portion of the binder, i.e., in a sandsize, or supersize; since experience has shown very little of the abrasive binder is worn away from the abrasive sheet in leather sanding operations before. the abrasive mineral grains are dulled beyond practical usefulness.

When employed in leather sanding operations, and other abrading operations presenting similar difiiculties, such as plastic sanding and, to a somewhat lesser extent, wood sanding operations, our novel abrasive sheet structures are extremely fill-resistant. They can be employed for long periods, in many instances without necessity of being periodically brushed or otherwise mechanically cleaned, all the while remaining effective in producing the desired finish. Even where some filling or clogging ultimately results (as it inevitably must as the sheet wears out), our structures are readily cleaned, ordinarily by briefly wiping with a brush. In fact, after such brushing it is usually not even visually evident that the sheet had been filled; and to the untrained eye not even evident that the sheet had been used at all.

In describing our invention we are mindful that for more than 30 years others have employed certain polyols, e.g., glycerol, ethylene glycol and diethylene glycol, in abrasive binders for the purpose of plasticizing and/or flexibilizing the binder composition. In this regard see Carlton Patent No. 1,775,631 granted September 16, 1930,

on application filed March 13, 1926. More recently, the

specific examples of ONeil et al. Patent No. 2,805,136 granted September 3, 1957, disclose abrasive sandsize coatings employing diethylene glycol in the sandsize, without reference to the function such material performs.

Insofar as we are aware, no one prior to the present invention has ever discovered or appreciated the fill-resistant effect that such oxy-containing compounds as we employ can, if properly employed, produce in coated abrasive sheet structures. It is not strange, however, that such potential has remained unrecognized in the art (notwithstanding the prior use of polyols in the manner just mentioned for so many years). For substantially no beneficial result, as respects fill-resistivity in leather sanding, accrues in the sheet structures disclosed in these orin other prior art. For example, thestructures prepared by following examples of the aforesaid -Neil et 211. patent do not exhibit significant improvement in fillresistance in leather sanding operations over structures otherwise identical except for the omission of the diethylene glycol.

Having briefly described our invention, the same will now be more specifically illustrated with the aid of the following non-limitative examples.

Example I To one side of a Web of 130 lb. neoprene-treated cylinder paper was applied a 38% solution of hide glue at a wet coating weight of 10 grains per 4" x 6 (4 inch by 6 inch) sheet. The glue coated sheet was then electrostatically coated with 22 grains by weight of Grade 240 aluminum oxide mineral per 4" x 6" sheet. The coated web was then festooned in a 100 F. oven maintained at a relative humidity of 47 percent for 10 minutes to dry the glue make-coat. The web was then passed through squeeze rolls by which a sandsize composition was applied at a wet coating weight of 22 grains per 4" x 6" sheet. The sandsize adhesive previously had been prepared by blending 86.5 parts of a solution of an A stage base-catalyzed phenol-formaldehyde resin having 81% non-volatiles with 30 parts of glycerine, and 7.6 parts of water, all by weight. The viscosity of this sandsize composition was approximately 360 cps. at 125 F. as measured by a Brookfield Viscometer.

The web was then again hung in festoons and the sandsize precured by heating in an oven for 18 minutes at 160 F., 108 minutes at 200 F., and 18 minutes at 190 F. The procured material was taken down from the festoons and wound into drum form with two layers of cheese cloth interposed between the convolutions. Final cure of the coated abrasive web was then effected by heating the drum for 1 hour at 150 F., 2 hours at 175 F., and 5 hours at 200 F. On a volume basis, the ratio of abrasive binder to abrasive mineral in the sheet structure of the present example is 3.16: 1. When tested, the abrading surface of the resulting sheet material was found not to be receptive to or readily wet by neats-foot oil, the oil forming in small droplets on the surface at a very high contact angle.

An endless belt having a width of 50 inches and a length of 103 inches was formed from the cured coated abrasive sheet material, and used on a belt sander conventionally employed in leather finishing operations. The contact cylinder over which the belt passed was made of 45 durometer rubber having serrations /8 inch wide spaced inch apart and extending at an angle of 25 to the side of the contact drum. The belt travelled at a rate of 5200 feet per minute, and leather sides were fed through the machine at a rate of 60 feet per minute. No noticeable filling of the belt by the abraded leather particles occurred for more than 4 hours, during which aoaaevs over 2200 leather sides had been processed. When some filling ultimately did occur, the dust was easily removed With a compressed air blast.

In contrast with the results achieved by our novel sheet structures of the present example, a coated abrasive sheet having the same mineral grade composed of conventional materials of conventional total binderzmineral ratio was found to have filled and clogged in only 4 minutes after processing only 30 sides. The total binder:mineral ratio of such a conventional structure is in the order of 1.32:1. Furthermore, a structure formed of materials identical to those of the present example, except for the omission of the glycerine, and containing a total binder:mineral ratio of 3.6 :1 (identical to that of the present example) also quickly fills with leather particles and is unsatisfactory. On the other hand a sheet'structure identically formed of the same materials as the abrasive sheet of the present example, except having a much lower total binderzmineral ratio, viz., 1.32:1, performs very similarly to the abovementioned conventional sheet having a total binder-mineral ratio of an identical 1.32: 1.

The proper ratio of binder to mineral in an abrasive sheet structure containing a particular grit and grade of mineral particle, type of backing, etc. varies greatly from that of a different sheet structure where a difierent grit or grade of mineral particle, or type of backing or both are employed. The method by which the mineral particles are applied also affects the required ratio. These variables and others which combine to determine the requisite or optimum binderrmineral ratio in any specific structure, present a situation which essentially defies direct accurate and inclusive generic definition of total binder:mineral ratio desired in the structures hereof. Nevertheless, there is a satisfactory and predictable procedure for determining the proper amount of abrasive binder in sheet structures hereof. This procedure involves a reflectance test by which the degree to which the abrasive binder fills around the abrasive grains can be determined. It is noted that the man at the abrasive maker has, for many years, held abrasive sheets at an angle to light, and in this way qualitatively determined, by the glossiness of the sheet, whether approximately the correct amount of binder, for his purpose, is present.

Instead of relying on qualitative visual examination methods of the past, we employ a far more precise and quantitative test, viz., ASTM test D523-5 1, entitled standard method of test for 60DEG specular gloss. In this test a beam of light rays is directed toward the sheet to be measured at an angle of 60 to a line perpendicular to the sheet. A photoelectric cell, also at an angle of 60 to the perpendicular, measures the amount of light which is reflected from the sheet and received by the cell. An ideal completely reflecting perfect mirror is assigned a value of 1000. Reflection apparently occurs primarily -from the upper surface of the sandsize adhesive, and the greater the resin:mineral ratio for any specific type of sheet the greater the reflectance. Measuring the reflectance, however, integrates the finished characteristics of the sheet, taking into consideration the various dififerences necessitated by the particular raw materials employed and the manner in which they are associated. By and large it makes little difierence in the resultant reflectance value of an abrasive sheet whether the binder or sandsize is filled or unfilled, or whether it is one type of resin or glue as opposed to another. Thus the refiectance of the sheet is essentially independent of whether the binder contains the oxy compounds we employ in the structures hereof.

By the test the 60 specular gloss value for the coated abrasive sheet of this example was 10.5 units. The conventional product referred to in the example hereinabove containing a total binder to mineral ratio of about 1.32:1, exhibited a gloss value of only 0.8. We have found that for the oxy-containing composition properly to demonstrate the unique fill-resistant characteristics in our structures the total binderzmineral ratio should at least equal a level exhibiting a gloss value of about 5 units. Of course, the ratio of total binder to mineral should not be so great as to flood the sheet or to bury the abrasive mineral grains to an extent where the useful aggressiveness of the abrasive surface of the sheet is lost. It has been found that sheet structures hereof, wherein the abrasive binder to mineral ratio is at a level demonstrating a gloss value of 30*33 are useful though we generally prefer to employ the binder at somewhat lower levels. For example, in sheets containing the coarser grades of mineral employed in leather-sanding, e.g., grade 120, We prefer the gloss value to be in the range of about 6-12. In sheets containing finer grades of mineral, e.g., grades 280 or 400, a gloss value in the range of about 9-18 is preferred.

The present example illustrates the use of a monomeric polyhydric alcohol as the oxy-compound in the binder. Many other polyhydric compounds are equally suitable, the various aliphatic glycols being especially suitable. The following example illustrates the use of higher monomolecular weight polymeric ether alcohols as the oxycompound.

Example 11 An adhesive was prepared by blending 86.5 parts of A stage phenolic resin containing 81% non-volatile material, 30 parts of polyethylene glycol having an average molecular weight of 1540, and 7 parts of water, all by weight.

A conventional Grade 280 aluminum oxide coated abrasive sheet material having a hide glue bond make coat on a 130-lb. neoprene-treated cylinder paper backing and a phenolic resin sandsize (total binderzmineral volume ratio of 1.32:1) was supersized with the adhesive com-. position described in the preceding paragraph at a wet coating weight of 14 grains per 4" x 6" sheet. The said coated abrasive sheet material (without the supersize) is sold commercially by the Minnesota Mining and Mannfacturing Company, St. Paul, Minnesota under the trade designation Production Resinite Paper, E-Weight.

The thus suspersized sheet material was precured in festoons for 4 hours at 175 F., and finally cured in festoons for 1 hour at 150 F, 2 hours at 175 F, and 5 hours at 200 F. The cured product was then taken down from the festoons and flexed to render it more flexible.

The final ASTM glossmeter value, obtained using the test previously described, ranged from to 12' units. The adhesivezmineral volume ratio of the structure was 3.48:1.

An endless belt having a width of 11 inches and a length of 65 inches was fabricated from the material described in the preceding paragraph and mounted on a belt sander similar to that employed in leather sanding operations. The contact roll over which the belt passed was identical to that described in Example I and was driven at 2850 surface feet per minute. A conveyor belt mounted beneath the contact roll was used to transport leather test pieces through the machine at a rate of 40 feet per minute, the aperture between the surface of the abbrasive belt and the surface of the conveyor belt being set at .065 inch. A welting leather strip 6 inches x 47 inches x .128 inch was fed through this machine ten times. The surface of the leather was then observed to be uniformly napped, color-receptive, and extremely attractive. The small amount of leather detritus which adhered to the surface of the belt was readily brushed away.

In contrast to the belt of the present example, employed as described in the preceding paragraph, a Grade 280 belt, identical with that of the present example but containing no supersize treatment, was found undesirably to burnish the leather irregularly after only three passes. -By this time the sheet filled or clogged, and the leather particles which adhered to the surface of the belt could not be brushed free. Similarly, a conventional belt which was resized with unmodified phenolic resin to a reflectance comparable to that of the product described in the preceding 6 paragraph performed no better than the conventional sheet.

Although polyethylene glycols of all known molecular weights are extremely soluble in Water, and can be employed in structures of the present invention, various other of the fill-retarding oxy-compounds are only sparingly soluble in water, if soluble at all. In such cases solvents other than water preferably are used for incorporating the oxy-compound into the binder composition, care being taken to employ a solvent or dispersant which is compatible with the binder composition, solvent vehicle for the latter, and/ or the solution of the binder composition, as the case maybe. The vehicle for the oxy-compound also can be the same as that for the-binder. For example, when polypropylene glycol having an average molecular weight of 2025 is employed, ethylene glycol monoethyl ether (Cellosolve) is employed as a common solvent for the oxy-compound and the phenol-aldehyde binder composition.

Example 111 A special binder composition was'prepared by employing an ether derivative of a polyether. Ten parts of Tergitol Non-ionic NP35 (an alkyl phenyl ether of polyethylene glycol manufactured and sold by Union Car-- bide), 2 parts of water, and 111 parts of liquid A stage. phenolic resin containing 81% non-volatile material, all by weight, were blended together.

A commercial Grade 240 aluminum oxide coated abrasive sheet material having a pound neoprene treated cylinder paper backing, a hide glue bond adhesive and a phenolic resin sandsize adhesive (total adhesive: mineral volume ratio of 1.19: 1) was supersized with the composition described in the preceding paragraph at a wet coating weight of 15 grains per 4" x 6" sheet. Curing conditions were identical to those described in the preceding example, except that the final cure was made in roll form. The ASTM glossmeter reflectance of this material was 17, and the adhesive:mineral volume ratio was about 3.04: 1.

The product of this example was flexed by passing it over a 1 inch steel bar while supporting the face of the material with a rubber roll. Endless belts were fabricated and tests conducted in the same manner described in the preceding example. After 10 passes of a strip of welting leather, no burnishing had occurred, and the leather strip was uniformly downy and color-receptive. The few leather particles which superficially adhered to the surface of the belt could be readily brushed oif.

Example IV A coated abrasive sheet like that described in connection with Example I was prepared except only four parts of glycerine were incorporated into the sandsize composition. The sheet was then coated with the sandsize composition and cured as described in Example I. The cured sandsize composition of the resulting sheet thus contained only about 5 percent by weight of the oxy-compound. The resulting structure was found to be a satisfactory fillresistant sheet in leather sanding operations.

The amount of oxy-compound contained in the binder at the surface of the sheet, as the present example indicates, is not particularly critical. A significant amount of the oxy-compound should be present. =We have found that at least a few percent, for example in the order of about 5 percent or less by weight of the various oxy-compounds hereof is suflicient to produce satisfactory results. On the other hand, little or no advantage seems to accrue from employing the oxy-compound in amounts greater than about 30-40 percent. Further, the oxy-containing compounds are not in and of themselves effective abrasive binders. Thus when employed in very high amounts the oxy-containing compound can diminish the desired quali-- ties of the binder within which the oxy-compound is in-- corporated. The amount and type of oxy-compound usedv preferably is selected so that no reaction occurs between; it and the binder to produce a reactionproduct having;

7 properties, such as permanent tackiness, etc., inconsistent with those of a suitable abrasive binder. The two also should besufliciently compatible as to form into a uniform substantially stable essentially homogeneous association on the sheet.

A substantial amount of the oxy-compound incorporated with the binder composition ordinarily is extractable by solvent extraction procedures indicating that much of the oxy-compound exists in the sheet substantially in an unreacted state.

Although the preceding examples illustrate flexible abrasive sheet materials hereof containing abrasive grains in the intermediate grade ran es, this is because in the leather sanding industry, to which the examples hereof are especially directed, abrasive sheets are normally used which have grade sizes within range of from about Grade 120 through 320 and finer. However, the present inventionis not limited either to these ranges; for it also has marked utility in the coarser grade ranges, and also in the very fine grade ranges, particularly in other industrial fields.

Having now described our invention with the aid of numerous specific examples, it is not our intention to be limited thereto. Rather it is our intent to be limited only by the scope of thespecification and invention taken as a whole, including the appended claims.

What we claim is as follows:

1. A flexible coated abrasive sheet which is highly fillresistant to leather and similar materials comprising a flexible backing and abrasive grains firmly bonded thereto by a total binder present in a high binder to mineral ratio at a gloss value of 'at least about units, said binder comprising a synthetic resin including uniformly distributed therein at least at the exposed surface thereof an oxycontaining compound compatible with the remaining binder constituents and selected from the class consisting of aliphatic polyhydric alcohols and aliphatic polyethers.

2. A flexible coated abrasive sheet which is highly fillresistant to leather and similar materials comprising a flexible backing and abrasive grains firmly bonded there- .to by a totalbinder present in a high binder to mineral ratio at a gloss value of at least about 5 units, said binder at the surface thereof comprising a hardened phenol-aldehyde resin having uniformly distributed therein an oxycontaining compound compatible with the remaining binder constituents and selected from the class consisting of aliphatic polyhydric alcohols and aliphatic polyethers.

3. A flexible coated abrasive sheet which is highly fillresistant to leather and similar materials comprising a flexible backing and abrasive grains firmly bonded thereto by a total binder present in a high binder to mineral ratio at a gloss value within the range of about 6l8 units, said binder at the surface thereof comprising a hardened phenol-aldehyde resin having uniformly distributed therein an oxy-containing compound compatible with the remaining binder constituents and selected from the class consisting of aliphatic polyhydric alcohols and aliphatic polyethers.

4. A flexible coated abrasive sheet which is highly fill-resistant to leather and similar materials comprising a flexible backing and abrasive grains of grade range of from about to 400' finnly bonded thereto by a total binder present in a high binder to mineral ratio at a gloss value within the range of about 6-18 units, said binder at the surface thereof comprising a hardened phenol-aldehyde resin having uniformly distributed therein an oxycontaining compound compatible With the remaining binder constituents and selected from the class consisting of aliphatic polyhydric alcohols and aliphatic polyethers.

5. A flexible coated abrasive sheet which is highly fillresistant to leather and similar materials comprising a flexible backing and abrasive grains firmly bonded thereto by a total binder present in a high binder to mineral ratio at a gloss value of at least about 5 units, said sheet having a surface size coat comprising a hardened phenol-aldehyde resin having glycerine distributed therein.

6. A flexible coated abrasive sheet which is highly fillresistant to leather and similar materials comprising a flexible backing and abrasive grains firmly bonded thereto by a total binder present in a high binder to mineral ratio at a gloss value of at least about 5 units, said sheet having a surface size coat comprising a hardened phenol-aldehyde resin having an aliphatic glycol distributed therein.

References Cited in the file of this patent UNITED STATES PATENTS 1,980,151 Barringer Nov. 6, 1934 l,025,249 Shuey Dec. 24, 1935 2,251,437 Brown Aug. 5, 1941 

1. A FLELXIBLE COATED ABRASSIVIE SSHEET WHICH IS HIGHLY FILLRESISTANT TO LEATHER AND SIMILAR MATERIAL COMPRISSING A FLEXIBLE BACKING AND ABRASIVE GRAINS FIRMLY BONDED THERETO BY A TOTAL BINDER PRESENT IN A HIGH BINDER TO MINERAL RATIO AT A GLOSS VALUE OF AT LEAST ABOUT 5 UNITS, SAID BINDER AT THE SURFACE THEREOF COMPRISING A HARDENED PHEONL-ALDEHYDE RESIN HAVING UNIFORMLY DISTRIBUTED THEREIN AN OXYCONTAINING COMPOUND COMPATIBLE WITH THE REMAINING BINDER CONSTTITUENTS AND SELECTED FROM THE CLASS CONSISTING OF ALIPHATIC POLYHDRIC ALCOHOLS AND AL IPHATIC POLYETHERS. 